A speech signal processing device equipped with a plurality of microphones and configured to accept a speech signal inputted via each of the microphones and process the accepted speech signal is known.
As one of speech signal processing devices of this type, a speech signal processing device described in Patent Document 1 acquires, for each frequency, power (an amplification factor corresponding to power) representing the intensity of a speech sound represented by a speech signal accepted via a certain microphone. Then, the speech signal processing device determines whether power acquired at one moment (acquisition power) corresponds with predetermined reference power for each frequency. In the case of determining that the acquisition power does not correspond with the reference power, this speech signal processing device determines that the microphone is out of order.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. JP-A 2002-159098
The plurality of microphones are arranged at mutually different positions. Therefore, the time when a speech sound generated at a certain position reaches each of the microphones varies with the microphone. In other words, at a certain moment, speech signals based on speech sounds generated at mutually different moments are inputted into the respective microphones.
Therefore, for example, in a case that the speech signal processing device is configured to use, as reference power, the power of a speech signal (a reference speech signal) accepted at a certain moment via a certain microphone (a reference microphone), there is fear that a speech signal as the source of acquisition power relatively largely differs from the reference speech signal.
In order to handle this, it is considered preferable to configure the speech signal processing device so as to use the average of power acquired at a plurality of moments as the acquisition power and the reference power.
Further, the power of background noise changes as time goes on. Therefore, also in a case that the speech signal processing device is configured to acquire the acquisition power and the reference power based on background noise, it is considered preferable to configure the speech signal processing device so as to use the average of power acquired at a plurality of moments as the acquisition power and the reference power.
However, in a case that the speech signal processing device is thus configured, for example, the speech signal processing device acquires the same acquisition power P0/N both when acquiring power P0 N-times and when acquiring power P1 smaller than the power P0 by a predetermined amount ΔP and power P2 larger than the power P0 by the predetermined amount ΔP N/2-times, respectively.
In other words, in this case, there is a problem that the speech signal processing device cannot determine with high accuracy whether power acquired when a predetermined reference speech signal is inputted corresponds with predetermined reference power.